Following the success of concrete paving solutions manufacturer Bosun’s redesigned Figure 8C castle bottom kerb, the company is now planning to also produce Figure 7 and Figure 3 barrier kerbs with castle bottoms.

Bosun has already ordered the required equipment from its Germany-based supplier to enable it to add the two new products to its range.

“We expect to start production of the Figure 7 semimountable and Figure 3 Bosun castle bottom kerbs in early 2013,” notes CEO David Wertheim Aymes.

The company launched the Figure 8C castle bottom kerb, which features cavities across the bottom of their surface to allow for easier handling and installation, in May.

The kerbs are manufactured in two lengths – 300 mm and 1 000 mm. Both lengths have a width of 300 mm and a height of 200 mm. The 300-mm-long kerb weighs about 36 kg, while the 1 000-mm-long kerb weighs about 107 kg.

Wertheim Aymes says Bosun found that when they were installed at road construction sites, the castle bottom kerbs were about 40% quicker to install than conventional kerbs.

“When installing conventional kerbs, if the screed surfaces are uneven, installers are forced to lift, refill and relay the kerb. With a castle bottom kerb, it is easier to manoeuvre it into place, as the screed is displaced by the cavities of the kerb, allowing it to sink into the screed,” he explains.

This, in turn, provides better adhesion and has more points of sure bonding, he adds.

Further, the castle bottom kerb, designed and manufactured at the Bosun facility, in Midrand, is less prone to movement than flat kerb surfaces.

Flat bottom kerbs also do not have consistent support from the screed. In some cases, critical areas of the surface may not be in contact with the screed, resulting in kerb breakages once weight is applied from above.

The regular points of sure bonding of the castle bottom kerbs and their proximity to one another negated this possibility, says Wertheim Aymes.

He says that, since their launch, the kerbs have been installed on a variety of roads, such as provincial and municipal roads, on existing road upgrades, as well as on new roads from Orange Farm, about 45 km south of Johannesburg, to lifestyle development Steyn City, located along the Jukskei river, in Johannesburg.

Bosun directly and indirectly supplies various local governments with paving and kerbs. These include the City of Johannesburg, the City of Tshwane, the Nelson Mandela Bay metropolitan municipality and various smaller municipalities like the Gert Sibande district municipality and the Steve Tshwete local municipality, in Mpumalanga.

Kerbs prevent drivers from parking or driving on areas beside a road, while mountable kerbs make it possible for vehicles to access these areas. Kerbs also provide structural support to the pavement edge and prevent the degradation of road edges. They also channel runoff water into storm drains.

Wertheim Aymes says kerb manufacturers should adhere to the SANS 927 specification for precast kerbs, but adds that it is also important to note the way in which kerbs are manufactured.

In Europe, kerbs have for decades already been manufactured in the dry cast method, whereas, in South Africa, kerbs have traditionally been produced by means of casting a wet concrete mix in moulds, which is then left to cure and then demoulded.

Large stones and other aggregates tend to settle very close to the surface of the kerb and, with slight abrasion to the kerb, the unsightly aggregates are exposed.

Wet cast manufacturing also requires vibration to eliminate air pockets from forming in the concrete. If this is not done for long enough, pin holes form on the surface of kerbs, potentially negatively affecting the quality of the kerbs, he explains.

In addition, the manufacturer’s production capacity is limited by the number of moulds available.

With the dry cast method, a block-making machine forms, compacts and vibrates a dry concrete mix into shape instead of using moulds to form the shape.

Casting production is not restricted by the number of available moulds and Wertheim Aymes says this ensures a reliable supply for all its customers.

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